cell differentiation and gene expression

Question 1

what is the difference between differentiation and modulation?

Answer 1

differentiation : a stable complex change

modulation : a temporary simple change

Question 2

what is cell differentiation?

Answer 2

the production of different cell types within an organism

Question 3

what is determination?

Answer 3

The stability of cell differentiation even after cessation of an inducing signal

Question 4

what are the segments of an embryo called?

Answer 4

somites

Question 5

what is gene expression?

Answer 5

the whole process leading to the synthesis of a final product of a given gene either a protein or a functional RNA like tRNA

Question 6

what is modulation?

Answer 6

when cells respond to their external environment/

Question 7

what is an example of modulation?

Answer 7

→in hepatocytes if alcohol is present they will produce ADH (alcohol dehydrogenase) which breaks down the alcohol.
→This enzyme will stop being produced if there is no more alcohol present

Question 8

what is modulation also known as?

Answer 8

adaptation

Question 9

How did the dolly the sheep experiment prove that all differentiated cells have the complete genome not just the genes they require?

Answer 9

A differentiated epithelial cell of the sheep was fused to the cytoplasm of the sheep oocyte and the cell proliferated to form an embryo. The differentiated cell had all the genes needed to form a sheep/

Question 10

what is a program of differentiation? and how is it controlled?

Answer 10

→ diverse set of cell-type-specific genes that are generally activated in expression during one step in lineage, while others are repressed.
at the level of mRNA transcription

Question 11

what are DNA probes?

Answer 11

pieces of synthetic DNA with a known sequence that is complementary to the sequence that you are looking for

Question 12

what are the two mechanisms for the control of gene expression?

Answer 12

chromatin remodelling and specific transcriptional regulation

Question 13

what are the two configurations of chromatin and how are they different?

Answer 13

→heterochromatin and euchromatin

→heterochromatin is the folded methylated version of DNA

→euchromatin is the unfolded transcriptionally active DNA .

Question 14

how does methylation occur?

Answer 14

→ strands are separated and there is new strand synthesis, each methyl group gets separated.

→New strand synthesis happens and there are two new strands which are unmethylated

→maintenance methyltransferase adds new methyl groups onto the daughter strands.

→This is how the methylation pattern is remembered in daughter cells.

Question 15

where does DNA methylation occur and why?

Answer 15

→DNA methylation occurs in stretches of DNA that are rich in CpG pairs which coincide with the promoter regions.

Question 16

how can unmethylated CpG pairs become methylated?

Answer 16

→CpG pairs are not always methylated, unmethylated pairs can become methylated during gamete formation and this is done by de novo methyltransferase.

Question 17

what effect does methylation have and give an example of a gene that is mostly methylated and why

Answer 17

→ increasing folding and silencing the gene.

→Globin genes are only needed to make haemoglobin so these genes are methylated in all other cell types of the body
→ the transcriptional machinery cannot access it.

Question 18

what is the difference between a promoter and an enhancer?

Answer 18

→enhancer increases the level of transcription of a gene →promoter initiates transcription of a gene.

Question 19

what are master gene regulators?

Answer 19

→ regulate transcription of a whole set of lineage-specific genes (a ‘program’) for a given cell type.

Question 20

how do master gene regulators work?

Answer 20

→Transcription of the gene for the master gene regulator occurs

→ creating the regulatory proteins

→These proteins then bind to and activate the promoters of different genes coding for proteins that will differentiate the cell.

→these specialised proteins are made, and then proceed to work on the cell.

Question 21

what are the three patterns of cell division and give examples

Answer 21

→Cells can divide very little but they divide to repair damage e.g endothelium cells or hepatocytes

→Cells that cannot divide (terminal differentiation) they are not replaced when they are lost, neurons and lens cells.

→cells that do not divide but they die and can be replaced by somatic stem cells, for example, red blood cells, gut epithelium cells and epidermal cells.

Question 22

what are some non lethal birth defects due to differentiation?

Answer 22

→aniridia - lack of the iris due to a mutation in PAX6

→Congenital anaemia and thrombocytopenia (platelet deficiency) due to a mutation in a transcription factor called GATA 1